The present invention relates to a disk drive unit and a disk device having this drive unit, and more particularly to a hydrodynamic fluid bearing unit for the disk drive unit.
Recently, in order to achieve the high-speed transfer of data and high-density recording, a motor in a magnetic disk drive unit has been more and more required to achieve a high-speed, high-precision rotation. In order to meet this requirement, a motor (as disclosed in JP-A-5-336696, JP-A-8-189525 and JP-A-9-200998), having a hydrodynamic bearing, has been proposed.
A motor in a magnetic disk drive unit is intensely required to have an improved shock resistance so that the function of the disk drive unit will not be deteriorated when a personal computer, incorporating the disk drive unit, is dropped from a desk or is fallen while it is carried.
Particularly, a notebook-type personal computer can undergo an impact force of about 1,000 G while it is used or carried, depending on the manner of handling it. And besides, since the notebook-type personal computer is driven by a battery, it requires a disk drive unit of the low power consumption-type.
A groove bearing, wherein shallow grooves for producing a dynamic pressure are formed in a spindle, is proposed in JP-A-5-336696. Although this groove bearing is excellent in high-speed operation and in accuracy of the spindle rotation, it has problems that the production cost is high and that the mass production can not be easily carried out. The depth of the dynamic pressure-producing grooves in the groove bearing are several microns, and when the grooves are deformed by an impact load, the adequate dynamic pressure cannot be produced, which results in a possibility that the unstable vibration occurs. A hydrodynamic three-lobe bearing, disclosed in JP-A-8-189525 and JP-A-9-200998, can achieve high-speed, high precision rotation equivalent to that obtained with the above groove bearing. However, when an impact force of about 1,000 G acts on this bearing, edge portions of the grooves can be deformed, so that its bearing characteristics are deteriorated.
JP-A-8-189525 discloses a groove-type thrust bearing. When a bearing surface of the groove-type thrust bearing is deformed by an impact force, it is liable that a lubricating fluid is not-properly supplied to the bearing surface.
The groove-type bearing supports or bears a thrust load at an end surface of a spindle or bearing, and therefore is subjected to a larger friction loss as compared with a ball bearing-type, and it is difficult to achieve a low power consumption design.
With the above problems of the prior art in view, it is an object of this invention to provide a disk drive unit provided with a bearing unit which has a small friction loss, and is excellent in shock resistance and mass production efficiency.
Another object of the invention is to provide a magnetic disk device provided with the above disk drive unit.
According to one aspect of the present invention, there is provided a disk drive unit comprising:
a rotary member having a spindle;
an information-recording disk being fixedly mounted on said rotary member;
a bearing unit rotatably supporting the spindle, the bearing unit including
a radial bearing device provided in opposed relation to an outer peripheral surface of the spindle, the radial bearing device having a concentric arc-shaped bearing surface that is concentric with the circular outer periphery of the spindle, and a non-concentric arc-shaped bearing surface that is non-concentric with the circular outer periphery of the spindle, and
a thrust bearing device provided in opposed relation to a distal end surface of the spindle;
a motor for imparting a rotational force to the spindle; and
a lubricating fluid filled in the bearing unit.
The maximum distance between the spindle and each of the non-concentric arc-shaped bearing surfaces is 1.5 to 3 times larger than the distance between the spindle and each of the concentric arc-shaped bearing surfaces.
The distal end surface of the spindle is formed into a flat surface, and the thrust bearing device has a flat surface which is smaller in diameter than the spindle, and is held in opposed relationship with the flat distal end surface of the spindle.
In one form of the invention, the distal end surface of the spindle is rounded, and the thrust bearing device has a flat surface held in opposed relationship with the rounded distal end surface of the spindle.
In another form of the invention, the distal end surface of the spindle is rounded, and the thrust bearing device has a concave surface which is substantially complementary to the rounded distal end surface of the spindle, and is held in opposed relationship with the rounded distal end surface.
In one form of the disk drive unit of the invention, the radial bearing device comprises a plurality of radial bearings arranged in a direction of an axis of the spindle, and at least one of the plurality of radial bearings has only the concentric arc-shaped bearing surface, and each of the other radial bearings has a plurality of the non-concentric arc-shaped bearing surfaces and axial grooves each formed between the associated adjacent non-concentric arc-shaped bearing surfaces.
In another form of the disk drive unit of the invention, the radial bearing device comprises a plurality of radial bearings arranged in a direction of an axis of the spindle, and each of the plurality of radial bearings has a plurality of the concentric arc-shaped bearing surfaces, a plurality of the non-concentric arc-shaped bearing surfaces and axial grooves each formed between the associated adjacent non-concentric arc-shaped bearing surfaces, and the plurality of concentric arc-shaped bearing surfaces of the radial bearing extend ⅙ to xc2xe of an inner peripheral surface of the radial bearing in a circumferential direction.
Preferably, the plurality of concentric arc-shaped bearing surfaces of the radial bearing extend about ⅓ of the inner peripheral surface of the radial bearing in the circumferential direction.
When viewed in a direction of an axis of the spindle, each of the plurality of concentric arc-shaped bearing surfaces is disposed substantially centrally between the associated adjacent axial grooves. Alternatively, each of the plurality of concentric arc-shaped bearing surfaces is disposed adjacent to the associated axial groove.
According to another aspect of the invention, there is provided a disk device comprising:
a rotary member having a spindle;
an information-recording disk being fixedly mounted on the rotary member;
a bearing unit rotatably supporting the spindle, the bearing unit including
a radial bearing device provided in opposed relation to an outer peripheral surface of the spindle, the radial bearing device having a concentric arc-shaped bearing surface that is concentric with the circular outer periphery of the spindle, and a non-concentric arc-shaped bearing surface that is non-concentric with the circular outer periphery of the spindle, and
a thrust bearing device provided in opposed relation to a distal end surface of the spindle,
a motor for imparting a rotational force to the spindle;
a lubricating fluid filled in the bearing unit;
a read/write head disposed in opposed relation to the information-recording disk; and
an actuator for positioning the head on said information-recording disk.